305 Paleontology and the Recapitulation Theory. By E. R. Cumings. I. In reply to a severe critique of the recapitulation theory, or biogenetic law. by Hurst (30), Bather remarks that "If the embryologists had not forestalled them, the paleontologists would have had to invent the theory of recapitulation." (1) This may be considered as a fair sample of the general attitude of paleontologists of the Hyatt school, to which Bather belongs, toward the recapitulation theory. Even the more conservative paleontologists, while inclined to use the theory cum grano salts, recognize the weight of evidence that Hyatt and his coworkers in the realm of paleobiology, have brought together, as is evidenced by the following quotation from Zittel (65) : "Nevertheless embyrcnic types are not entirely wanting among invertebrates. The Pale- ozoic Belinurida? are bewilderingly like the larvae of the living Limulus. The pentacrinoid larva of Antedon is nearer many fossil crinoids than the full grown animal Among pelecypods the stages of early youth of oysters and Pectinidse may be compared with Paleozoic Aviculida?. Among brachiopods, according to Beecher. the stages which lhing Tere- hratulida* pass through in the development of their arm-skeleton correspond with a number of fossil genera. The beautiful researches of Hyatt, Wiir- tenburger and Branco. have shown that all Ammonites and Ceratites pass through a goniatite stage, and that the inner whorls of an Ammonite con- stantly resemble, in form, ornament and suture line the adult condition of some previously existing genus or other." In violent contrast with this full acceptance, or this guarded ac- ceptance of the theory on the part of the paleontologists, is the position of a considerable school of embryologists and zoologists. Perhaps no one lias put the case against the theory more baldly and forcibly than Mont- gomery in his recent book on "An Analysis of Racial Descent" (42). He says: "The method is wrong in principle, to compare an adult stage of one organism with an immature stage of another." And again: "There- fore we can only conclude that the embryogeny does not furnish any re- capitulation of the phylogeny. not even a recapitulation marred at occa- [20—230031 306 sional points by secondary changes. An analysis of the stages during the life of one individual can in no way present a knowledge of its ancestry, and the method of comparing non-correspondent stages of two species is wrong in principle." Equally sweeping is the statement of Hurst (30) : "The ontogeny is not an epitome of the phylogeny, is not even a modified or 'falsified' epitome, is not a record, either perfect or im- perfect of past history, is not a recapitulation of evolution." It would seem as though two statements could not be more flatly con- tradictory than these of Hurst and Montgomery, and that of Bather quoted above. Nevertheless I venture to make the seemingly paradoxical asser- tion that both parties to the controversy may be right, for the simple rea- son that they are talking about quite different things. This has been nowhere better expressed than by Grabau (25). He says: "It has been the general custom to test the validity of the recapitulation theory by the embryological method; i. e.. the comparableness of the changes which the individual undergoes during its embryonic period to the adults of more primitive types. Usually the comparison has been with the adults of ex- isting types, since in most eases these alone were available for compari- son. It is no wonder, then, that such comparisons have led to innumer- able errors, if not absurdities, which have placed the recapitulation theory in an evil light and awakened in the minds of many serious investigators doubts as to the validity of the deductions based upon this doctrine. When, however, the entire life history of the individual is considered, instead of only the embryonic period, and when the successive stages of epembryonic development are compared with the adult characters of related types, in immediately preceding geologic periods, it will be found that the funda- mental principle of recapitulation is sound, and that the individuals do repeat in their own epembryonic development the characters of their own immediate ancestors." (Italics mine.) It is as a matter of fact true that the Hyatt school of paleontologists have based their phylogenies on epembryonic rather than embryonic stages —stages beginning with the nepionic or infantile—since in the nature of the case the true embryonic stages are scarcely ever accessible to the stu- dent of fossils. It is no less tine that the severest critics of the theory of recapitulation have rested their case largely en the real or supposed lack of correspondence between the embryonic stages and the adult stages of assumed ancestors, or upon certain a priori considerations having to 307 do with the laws of development and inheritance. To the former class belong such critics as Von Baer, and to the latter class such as Hatschek, His, Hurst, Montgomery and others. In making this statement I am aware that paleontologists sometimes compare true embryonic stages with adult stages of pre-existing types. As examples of this we might cite the comparison of the larval stage of Antedon with adult Paleozoic crinoids, as mentioned by Zittel; and the classic attempt of Beecher to reconstruct the ancestor of the Brachiopoda by a comparison of the phylembryonic stages of a representative series of genera of recent and fossil brachiopods. Nevertheless by far the greater number of comparisons that have been instituted by paleontologists have been between epembryonic stages of individuals and adult stages of older forms. Such comparisons are those of Hyatt, Branco, Karpinsky, Wiirten- burger, Bnckman, Neuinayr, Smith, Beecher, Clarke and others among the Cephalopoda ; of Beecher and Schuchert, Raymond, Greene and Cumings amoug the Brachiopoda ; of Jackson among the Pelecypoda ; of Grabau and Burnett Smith among the Gastropoda; of Lang and Cumings among the Bryozoa ; of Ruedemann among the graptolites ; and of Beecher, Girty, Lang and others among the corals. To many of these researches I shall refer later. I am also not unmindful of the fact that many of those who are not primarily paleontologists recognize the fact that development does not terminate with the completion of the embryonic stages, and that recapitu- lation may be legitimately looked for in epembryonic as well as embryonic stages, or that it may be sought iu epembryonic stages, even though masked or falsified in embryonic stages. It is true, of course, that some speak of a comparison of ontogeny and phylogeny when, judging by the context, they mean a comparison between embryogeny and phylogeny. There arises here a question of definition : does the biogenetic law mean that the ontogeny is a recapitulation of the phylogeny, or does it mean that the embryogeny is a recapitulation of the phylogeny? If we take the general consensus of opinion we shall find for the former definition, and if we take the words of Haeckel, whose statement of the law is the one usually quoted, we shall again find for the former definition. I believe that, as a matter of fact, no one would maintain that the second definition is cor- rect, however much he might forget in his studies to take the epembryonic stages into consideration. 308 Nor would I create the impression that the einbryologists and zoolo- gists have utterly deserted the paleontologists in their support of the re- capitulation theory. Several recent papers give considerable aid and com- fort to those of us who still believe in recapitulation. I shall introduce here the conclusions of three of these workers, more particularly because it will afford me an opportunity to correct what I hold to be another error of those who oppose the theory. One of the most interesting pieces of evidence that has recently been adduced in favor of the idea that ontogeny recapitulates phylogeny is to be found in a paper by Griggs on "Juvenile Kelps" (28). It is not my purpose, however, to discuss the very interesting evidence which he has recorded, but rather to quote his remarks on the views of His and Morgan, and his general conclusions. His maintains that the reason why ontogeny seems to recapitulate phylogeny is because the stages in development are. as Griggs paraphrases it, "only the physiologically necessary steps for the formation of the adult body from its earliest stage, which in most cases is the egg." With the ideas of Morgan as expressed in his valuable book on "Evolution and Adaptation" we are all familiar. He holds that or- ganisms repeat in their development, not adult stages, but only embryonic stages of their ancestors. To this idea he has given the name of "repe- tition." On this point of the recapitulation of embryonic conditions Griggs makes the following pertinent statements : "In the toothless animals, the whale and the bird, the development of teeth in the jaws is entirely un- necessary * * * it may even be said to hinder the attainment of the adult condition. The same is true of the mammalian gill slits and of most structures which have in the past attracted attention in connection with the recapitulation theory. As the ancestral period when such struc- tures were fully developed in the adult becomes more and more remote, the tendency to inherit them becomes less and less, because of the cumu- lative impulses given to the heritage by the nearer ancestors. Conse- quently they are successively less and less developed. Any gradual' loss of inheritance can, in the nature of the case, take place only from the mature condition backward toward the beginning of the life cycle ; other- wise we should have adult structures with no ontogenetic history.